This invention relates to an electronic taximeter in which an electronic calculator calculates a fare based on distance and time and constant data representing a tariff stored in a constant store so that the fare may be indicated by a display, and uses a device for programming the constant generator.
As known, a taximeter is used in a taxi to calculate a fare on the basis of the services rendered. The basis for calculating the fare are increments of distance and/or increments of waiting time. For adapting the meter to locally differing conditions, the distance and time increments are multiplied by a factor, the so-called tariff, and the fare is continuously determined in a calculating device and indicated by a display. During a trip, the meter develops and displays the total fare by summing the predetermined fare increments and advancing the display to higher values by the predetermined fare increments. The tariff regulations also provide a base or initial fee for securing a minimal amount for a trip that has been started. When services go beyond the usual scope, calculating the fare on the basis of distance and time is insufficient, and so-called additions or extras, which are normally debited as fixed amounts, are added to the sum of the fare units at the end of a trip. Separate memories (RAMs) store details, such as total trips made, total extras performed, total fare units, total distances travelled, distances with the taxi occupied, and the like for management purposes and for economic control. These data must therefore be available for evaluation at any time in an accessible form.
Electronic taximeters come in a whole line of embodiments which calculate basic fare increments by producing a pulse series representing the waiting time and another pulse series simultaneously representing distances. This is shown in German Patent Publications DE-OS 12 59 129, DE-OS 17 74 560, DE-OS 21 38 863. As a rule, the pulse series enter a binary reduction device which generates a pulse that then passes into a succeeding main counter which represents fare increments to be displayed. The reduction ratios set up in the binary reduction devices correspond to the local tariff valid at the place of use of the taximeter. This leads to a question of expenditure for any modification in the basic tariff data which are used for fare calculation. A modification in the tariff data of new values in the known devices would mean an alteration in the hard wired connections representing reduction ratios and set up in matrix form. Hence, for modifications, the taximeter must be taken out and after performing the alterations to the interior of the taximeter be remounted in the taxi. This means unjustified cost and lost time just for setting a new tariff in the taximeter.
In view of these disadvantages, basic tariff data have already been coded in an exchangeable programmable read-only memory (PROM) so that making tariff changes is accomplished by simply changing one module, that is the PROM. This makes possible an uncomplicated and quick modification in the taximeter of the new tariff data without removing the apparatus from the vehicle. (German Patent Publication DE-PS 22 02 865 illustrates the latter principle.) Such a PROM is a module whose elements irreversibly store the desired contents. This means that for each minor modification in the tariff structure, the module must be exchanged for a completely new module (PROM) that is adjusted to the newly modified tariff. Also, this solution is not quite satisfactory when considering that the tariff structure frequently may change, for instance, due to currency devaluations or changing locations of the taximeter which make it necessary to change the tariff PROM each time. Finally, the production and exchange of the new tariff store is permitted only by specially authorized persons or workshops which always accounts for considerable waste of time and money.
Another known embodiment for storing tariff data is described in German Patent Publication DE-OS 28 22 019. Here, the calculating arrangement of the taximeter is combined with a read-write store (RAM) of low current consumption so that new tariff data may be entered by an external device which is to be connected to the central processing unit (CPU) that communicates with the read and write store. The kind and specification of the read and write store make it possible repeatedly to modify the parameters defining the tariff. However, the big disadvantage of this known device is that carrying through a modification of the tariff data in the tariff store occupies much of the programming capacity of the calculating device. Apart from that, it is also necessary that the read and write store, according to this device, be continuously connected to a battery by means of an additional voltage control to provide a constant voltage supply. This means that, at each breakdown of the supply voltage of any kind, the tariff data store loses its content and the tariff data for determining the fare are forfeited.